1. Field of the Invention
This invention relates generally to electrically powered systems of the kind which may present various hazardous electrical shock risk conditions when operating in their intended environment. The invention relates more particularly to an electrical shock prevention method and system for preventing electrification of such an electrical system when any one or more of its associated electrical shock risk conditions exist.
2. Discussion of the Prior Art
As will become evident from the ensuing description, the present shock prevention invention may be utilized in a variety of electrical systems of the character described. The intended use of the invention, however, is in a swimming pool underwater lighting system for preventing hazardous electrification of the pool water. The invention will be described in this context.
Simply stated, a conventional swimming pool lighting system comprises a plurality of pool lights mounted in cavities in the pool side wall below the normal water level in the pool and an electrical circuit for electrifying these lights. Each light includes a generally cup-shaped lamp housing having an open front end, and a replaceable lamp, typically a 100 to 500 watt lamp, mounted within the open front end of the housing and sealed about its perimeter to the housing. Each lamp housing is removably fixed within its recess in the pool side wall, typically by means of a mounting ring which seats against and is secured to the front end of the lamp housing and to the pool side wall.
Electrical power is supplied to the several pool lights from an incoming power panel through a main power switch and an underground power cable having branches which enter and are sealed to the lamp housings. The cable contains three wire leads which are terminated within the interior of each lamp housing at the rear of the lamp in the housing. These three leads include a black high voltage lead, a white common lead, and a green ground safety lead which is grounded to earth in the power panel. The ground lead termination within each lamp housing is grounded to the housing if it is metallic or to some other metallic part of the pool light assembly. The black (high voltage) and white (common) terminations in each lamp housing are connected to the respective lamp through a short connector cable within the housing terminating in an electrical socket for receiving a coupling "plug" on the rear of the lamp. This plug consists of two electrical prongs connected to wire supports within the lamp which are connected to and support the ends of the lamp filament.
A swimming pool lighting system of this kind presents several potential shock risk conditions capable of electrifying the pool water at a lethal electrification level. These shock risk conditions include (1) a broken pool lamp, (2) a water leak in a lamp housing, (3) low pool water level, and (4) faulty wiring of the lighting system involving reversal of high voltage and common connections at some point in the system..
These shock risk conditions will be discussed in detail later. Suffice it to say at this point that shock risk condition (1) (broken lamp) involves breakage of the glass envelope of a pool lamp with resultant direct contact of the pool water with the lamp filament and its conductive supports. While the filament would certainly burn out or break upon contact with the water or air, the "high voltage" filament support, that is the filament support connected to the high voltage lead of the underground power cable, would directly contact and thus electrify the pool water. Shock risk condition (2) (water leak in a lamp housing) may occur due to leakage of the seal between a lamp housing and its lamp or to melting of a plastic lamp housing as a result of overheating of the housing. In either case, pool water entering the housing may contact an electrified conductor in the housing with resultant potentially lethal electrification of the pool water. Regarding shock risk condition (3) (low pool water level), swimming pool lights are designed to operate submerged in pool water which continuously cools their lamps and lamp housings. If the pool lights are left on for even a relatively brief period of time when the surface of the pool water is below the level of the lights, the heat generated by a pool lamp can easily overheat its housing. Such overheating can melt the lamp housing if it is constructed of plastic or damage the housing seals. In either case, the overheating damage may permit flooding of a lamp housing and thus create a potentially lethal shock risk when the pool is later filled to its normal level above the pool lights. Shock risk condition (4) (faulty wiring of the pool lighting system) involves inadvertent reversal of the high voltage and common lead connections at some point in the wiring system, such as at a pool light, thereby electrifying the common lead in one or all of the pool lights at a potentially lethal electrification level.